Dynamic Line Management (DLM) is a technique for improving the performance (in terms of stability, speed, latency or otherwise) of DSL connections. (NB The term “xDSL” is sometimes used to refer to any of an increasing family of DSL technologies, but the term “DSL” will in general be used here). DLM is particularly useful when operating DSL connections at close to their maximum speed, because under these conditions external noise affecting the transmitted signal can cause the transceivers to be unable to successfully recover the signal transmitted with sufficient reliability to enable the connection to be maintained. If this occurs, the connection needs to be re-established. This is referred to as a re-synchronisation (“re-synch”) or a re-train, and the user generally notices a temporary loss of service while the connection is re-established, which may take 30 seconds or more. Re-synchs are generally found to be particularly annoying by end-users using VoIP or video services, but are generally less noticeable to users simply browsing the web.
DLM seeks to minimise re-synchs by automatically analysing DSL connections (especially the rate of occurrence of re-synchs) and varying certain parameters which can affect the likelihood of re-synchs occurring (for example the depth of interleaving, the amount of redundancy built into the encoding used, etc.). Typically, this is done by using a number of different “profiles” having various different sets of values for the parameters most likely to have an impact on the performance (stability or otherwise) of DSL connections and moving a particular connection between different profiles until a profile is found which provides acceptable performance. The profiles are applied at the network equipment end of the access loop, usually within a piece of equipment known as a Digital Subscriber Line Access Multiplexer (DSLAM) which houses a number of DSL transceiver units as is well known in the art. This may be done at a local exchange (sometimes referred to—especially in the USA—as the Central Office), but may be done closer to the user premises (at a street-cabinet, for example, in “Next-Generation Access (NGA), for example).
Typically, the profiles can conceptually be thought of as ranging between “more aggressive” and “less aggressive”, where the more aggressive profiles tend to provide better services to the user in terms of especially higher bit-rates and lower latencies, but are more likely to result in the line being unstable, whereas less aggressive profiles tend to offer lower bit rates and/or higher latencies but greater stability.
Profiles need not be “predetermined”—in some cases, they may be generated or created from scratch or by modifying an existing profile in response to a determination that different operational parameters are likely to lead to better performance, for example.
Referring to prior disclosures, an Alcatel Technology White Paper from April 2005 entitled “Dynamic Line Management for Digital Subscriber Lines” previously available at: http://www1.alcatel-lucent.com/com/en/appcontent/apl/18812_DLM_twp_tcm172-228691635.pdf discusses DLM and suggests in overview an implementation in which there is a “Validation” phase and an “Operations” phase. In the Validation phase a connection is monitored fairly intensively to identify an appropriate profile for the line and thereafter it is monitored less intensively to ensure that the originally selected profile continues to remain valid.
International patent application WO2008/093045 describes an earlier DLM solution devised by the present applicants in which very unstable data connections are detected in an efficient manner and corrective action is taken within a relatively short period of time whilst data connections which are not very unstable are monitored and transitioned between different profiles based on more thorough monitoring over a longer time-scale.
DLM solutions such as those above use, as at least one of the metrics used in monitoring the performance of a line, the number of re-trains or re-synchs occurring on a line within a predetermined period of time. In view of the fact that this metric can in certain circumstances be misleading, International patent application WO2009/081131 proposed a technique intended to allow for a more reliable metric of line performance to be provided. The technique disclosed involves processing data on the number of re-trains or re-synchs occurring on a line within a predetermined period of time in order to take account of the possibility that some re-synchs may be caused (i.e. intentionally) by user action rather than as a result of the line experiencing technical problems or instability.
International patent application WO2012/042231 relates to a method of operating an access network in which a different profile from a plurality of stored profiles is selected and applied to a data connection between an end-user device and an aggregation transceiver device. The selection of a profile is done in dependence on an analysis of connection data relating to a monitoring period which itself comprises a plurality of shorter periods. The analysis is done in such a way as to discount indications of instability that have been obtained in respect of any shorter periods during which it is determined that the user was actually inactive.